The field of the invention relates generally to controlling aircraft in flight, and more specifically, to a method and system for computing a holding pattern flight path to meet a required holding pattern departure time.
In today's airspace, delays due to congestion are common. When the number of aircraft entering an airspace exceeds the number of aircraft that can be safely handled by the available Air Traffic resources (limited by the number of controllers and type of automation), delays are imposed on aircraft. These delays are typically achieved by instructing aircraft to reduce speed, using radar vectors, or by orbital holding. In the case of orbital holding, the Flight Management System (FMS) computes the track over ground as a sequence of straight segments and curves, in the form of a “racetrack”. The straight segment is typically a fixed time or, more frequently, a fixed distance, and the curved segment is flown at a constant bank angle or constant radius to transition from one straight segment to the next.
A problem with current holding operations is that the air traffic controller must estimate where and when to command the aircraft to leave the holding pattern in order to meet a time (for metering or merging with other aircraft in a defined arrival sequence) at a point after leaving the hold, such as within the arrival procedure. Due to the geometry of the holding pattern, it is difficult for the controller to estimate when the aircraft will leave the holding pattern or how long it will take the aircraft to reach the desired arrival point after leaving the hold, because of this uncertainty there is often a large amount of error between when the controller wants the aircraft to arrive at the desired point after leaving the hold and when the aircraft actually arrives there. Currently, air traffic controllers estimate, based on experience, using an average flight time to determine when to ask an aircraft to leave its current holding pattern. However, the flight time will vary significantly based on where the aircraft leaves the hold, introducing uncertainty which requires additional separation buffers. This uncertainty results in decreased capacity and increased fuel burn for following aircraft due to their increased time spent in the holding pattern.
At least some known methods to address this problem include a method to determine the shortest path to exit the hold. However, this method does not use a required crossing time or required exit time to compute the necessary hold path; its objective is simply to minimize the distance required to exit the hold.